Function find_generation_point 

pub fn find_generation_point(
    rng: &mut LegacyRandom,
    chunk_x: i32,
    chunk_z: i32,
    mtype: MineshaftType,
    sea_level: i32,
    min_y: i32,
    get_surface_height: &mut dyn FnMut(i32, i32) -> i32,
) -> MineshaftResult

Generates mineshaft pieces and returns the biome check position + piece data.